Caption: Sunspot mapping. German astronomer Christoph Scheiner (1575-1650) mapping sunspots with the help of an assistant during the early 1600s. Sunspots are dark areas on the Sun's surface caused by fluctuating magnetic fields within the Sun. Scheiner discovered the existence of sunspots in March, 1611. Although Galileo claimed to have observed the spots first, Scheiner continued his systematic study of the Sun for nearly sixteen years before beginning the publication of his great work, the 'Rosa Ursina' in the 1620s, which is now a standard treatise on the subject. It contains not only numerous observations, but also a detailed account of his methods and apparatus.